Solid oxide fuel cells (SOFCs) can potentially utilize hydrocarbon fuels without precious metal catalysts. As methane is the simplest hydrocarbon fuel and natural gas (with methane as the main component) is readily available, direct-methane SOFCs have attracted great attention and the catalytic activity of the anode materials plays an important role for this application. Among the non-precious metals, Ni shows impressive catalytic activity in steam-reforming methane, but suffers significant carbon deposition under low steam content which is mainly caused by methane thermal cracking. Such degradation can be mitigated by selection of appropriate catalyst supports and by control of the particle size, dispersion and stabilization of the metallic catalyst particles. However, these strategies are not suitable for the conventional Ni-cermet anode since it usually contains a large volume ratio of Ni to maintain sufficient electrical conductivity. This feature makes it easier for carbon formation to occur on the excessive Ni surface. Additionally, the large ratio of Ni tends to cause the anode sintering at high operating temperatures and more serious volume change during redox cycles.
Mixed ionic and electronic conductors (MIECs) have recently been explored as anode materials for direct-hydrocarbon SOFCs. However, the electrical conductivity and the catalytic activity of the most reported MIEC ceramics are still not satisfactory. Without precious metal catalysts, the cell performances are limited, especially when directly operated with hydrocarbon fuels.
Thus, improvements in anode materials are desirable.